Cholera toxin B (CTB) is one of the subunits of the cholera toxin, produced by the bacterium Vibrio cholerae. This toxin is responsible for the severe watery diarrhea characteristic of cholera. CTB is non-toxic by itself and consists of five identical subunits that bind to the GM1 ganglioside receptor on the surface of cells, facilitating the entry of the toxic A subunit into the cells.
